How is the hydrostatic end force on a flange calculated?

The hydrostatic end force is H = P × π/4 × G², where P is the internal pressure and G is the gasket mean diameter. This is the force trying to separate the flanges due to internal pressure.

What is the gasket reaction force?

The gasket reaction force is the minimum compressive load needed to maintain the seal under operating conditions. It depends on the gasket material, type, and the gasket factor 'm' from ASME PCC-1 or EN 1591.

How many bolts should a flange have?

The number of bolts depends on the flange size and pressure class. Standard flanges use 4, 8, 12, 16, 20, or 24 bolts arranged symmetrically. The bolt spacing should not exceed 2d+6t/(m+0.5) to ensure adequate gasket compression between bolts.

What is the difference between operating and seating conditions?

Operating condition includes both pressure load and gasket maintenance load simultaneously. Seating condition (gasket seating, no pressure) requires sufficient bolt load to initially seat the gasket and achieve a seal before pressurization.

Can I use this for ASME B16.5 flanges?

This calculator provides a simplified bolt load analysis. For ASME B16.5 standard flanges, the bolt loads are pre-calculated in the standard tables. For custom flanges or detailed analysis, use ASME PCC-1 or EN 1591-1 methods.

Free Engineering Tool

Flange Bolt Pattern Calculator

Calculate per-bolt load for a pressurized flanged joint with gasket. Enter pressure, gasket dimensions, and bolt configuration.

ASME PCC-1EN 1591Gasket Joints

Internal Pressure (MPa)

Gasket OD (mm)

Gasket ID (mm)

Number of Bolts

Gasket m Factor

Gasket y Factor (MPa)

Quick presets

Results

Per-Bolt Load (Operating)

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Total Bolt Load (Operating)

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Hydrostatic End Force (H)

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Gasket Reaction (Hp)

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Gasket Mean Diameter (G)

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Hydrostatic End Force

Gasket Reaction (Maintaining Seal)

Total Operating Bolt Load

G — gasket mean diameter = (OD + ID) / 2
m — gasket maintenance factor (ASME Table 2-5.1)
y — gasket seating stress (MPa)

Example — DN200 PN10 Spiral Wound

P=1.0 MPa, OD=273, ID=219, 8 bolts, m=2.0

G = (273+219)/2 = 246 mm

H = 1.0 × π/4 × 246² = 47,529 N

Hp = 2×1.0×π×246×(273−219)/2 = 2×1.0×π×246×27 = 41,737 N

W = 47,529 + 41,737 = 89,266 N

Per bolt = 89,266/8 = 11,158 N ≈ 11.2 kN

Flange Bolt Pattern Calculator | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026

Results

Hydrostatic End Force

Gasket Reaction (Maintaining Seal)

Total Operating Bolt Load